The wiring density of printed boards has been steadily rising in recent years because of the need for devices to be smaller and offer a higher performance. This has resulted in the wiring on boards being made finer, so the surfaces thereof have been made lower in profile. However, this trend toward lower surface roughness has made it difficult to achieve satisfactory adhesion between substrates and the metal plating films that are formed over the substrates. However, to meet the above-mentioned needs, a further increase in this adhesive strength will be also required.
Various proposals have already been made for how to handle this need. Of these, Patent Documents 1 and 2 disclose that a polyimide resin substrate material is coated with a polyimide resin precursor solution containing a palladium compound, this coating is dried to form a polyimide resin precursor layer, and then this product is irradiated with UV rays in the presence of a hydrogen donor to form nuclei for a primer plating layer, after which a primer plating metal layer is formed by an electroless plating treatment, then a surface plating layer is formed, before or after which the polyimide resin precursor layer is heated and imidized to create a polyimide resin layer. Forming the nuclei for the primer plating layer within the polyimide resin layer here provides an anchor effect that improves the adhesive strength between the polyimide resin layer and the plating substrate metal layer.    Patent Document 1: Japanese Patent Publication 2002-30216A    Patent Document 2: Japanese Patent Publication 2002-374055A